Automotive exhaust system using filter containing calcium carbonate coating

Abstract

Automotive exhaust gases, and especially the exhaust gases which have been further oxidized by a treatment in a catalytic converter, are treated by passing them through a filter containing paper coated with a calcium carbonate coating. The paper is desirably coated on both sides with heavy coatings and wound into a roll with spacers extending through the roll to permit the gases to pass therethrough. The calcium carbonate desirably constitutes at least 85% of the weight of pigments and fillers in the coating and the proportion of binder does not exceed 20% of the total weight of pigments and fillers. The acidic gases in the exhaust, and particularly the oxides of sulfur, react with the finely divided particles of calcium carbonate in the coating to form an ash which flakes off from the lower face of the roll while the gases pass upwardly through the roll.

I claim: 
     
       1. In an exhaust system for an internal combustion engine, the improvement comprising a filter contained in a container and interposed in the exhaust line, said filter containing paper formed into a gas filter in which the plane of the paper is parallel to the movement of the exhaust gases, said paper being coated with finely divided particles of calcium carbonate, said paper being ablative under the conditions encountered in said exhaust system, said calcium carbonate constituting at least 85% of the weight of pigments and fillers in the coating, and the proportion of binder in the coating not exceeding 20% of the total weight of pigments and fillers, and said filter being positioned so that when the exhaust gases are passed through the filter, the coated paper can fall away from the filter where it is initially contacted by said exhaust gases. 
     
     
       2. An exhaust system as recited in claim 1 in which the virgin fiber content of the paper is unbleached. 
     
     
       3. An exhaust system as recited in claim 1 in which the calcium carbonate coating is unfinished. 
     
     
       4. An exhaust system as recited in claim 1 in which said filter is horizontal with the coated substrate constituting the filter being vertical, and the exhaust gases are passed upwardly through the filter. 
     
     
       5. An exhaust system as recited in claim 4 in which a space is provided below the filter for the collection of ash. 
     
     
       6. An exhaust system as recited in claim 4 in which said filter comprises a roll of calcium carbonate-coated paper having spacers extending vertically through the roll. 
     
     
       7. An exhaust system as recited in claim 1 in which said paper is coated on both sides with said calcium carbonate coating, the coating weight exceeding 15 pounds per side per ream. 
     
     
       8. An exhaust system as recited in claim 7 in which said calcium carbonate coatings are unfinished.